Conventional oil-adsorbing compositions are generally in the form of a porous film or a granular material derived therefrom. When such an oil-adsorbing composition having an oily substance adsorbed thereon is mixed with various types of solvents, the composition releases the oily substance retained. In particular, when such an oil-adsorbing composition is mixed with water, the oily substance once adsorbed on the composition is readily released therefrom. Oil-adsorbing compositions that have the property of adsorbing an oily substance thereon or retaining an oily substance therein and then releasing the adsorbed oily substance in a solvent such as water can find a wide range of applications. Accordingly, its industrial use has been contemplated in various fields.
As a starting material component for the oil-adsorbing composition, a starch-derived substance has been attracting attention. This is because a starch-derived substance can find a wide variety of applications due to ease of processing, and no environmental damage caused by its incineration after oil adsorption. Conventionally, an oil-adsorbing composition having an oil adsorption property and oil retention ability is produced by a method comprising pouring an aqueous solution of a starch hydrolysate or a reduced starch hydrolysate between roll slits (drums) of a drum dryer; then boiling and drying the solution to form a porous film, and crushing and powdering the porous film (Patent Literature 1).
Patent Literature (PTL) 1 discloses that the oil-adsorbing composition thus obtained is highly soluble in water, and can smoothly release an oily substance when placed into water.